1. Field of the Invention
The invention relates to video-on-demand systems and, more particularly, the invention relates to a method and apparatus for generating a real-time video bitstream for transmission through a video-on-demand system as well as simultaneously storing the video information in a format that facilitates demand television, i.e., a play bitstream, a fast forward bitstream and a fast reverse bitstream that are derived from the real-time video bitstream content.
2. Description of the Background Art
In a video-on-demand system such as the OnSet™ system manufactured by DIVA Systems Corporation, a file server is used for streaming video information to users (subscribers) of the system. The OnSet™ system is described in U.S. Pat. No. 6,253,375, and the file server is described in U.S. Pat. Nos. 5,671,377 and 5,581,778. The disclosures of this application and these patents are incorporated herein by reference. The OnSet™ system contains service provider equipment coupled through an information distribution network to subscriber equipment. This system provides subscribers VCR-like controls to enable a subscriber to select information content, for example, a movie, then play, fast forward, rewind, pause, or stop the selected movie. The subscriber enters control commands through the subscriber equipment and the service provider equipment executes the commands to fulfill the purpose of the command, e.g., play, fast forward, rewind, stop or pause the movie.
A file server forms a portion of the service provider equipment and stores, for a given movie, a standard play stream (i.e., an MPEG-2 compressed video bitstream), a fast forward stream and a fast reverse play (rewind) stream. The fast forward and fast reverse streams are also MPEG-2 compressed video, where the fast forward stream is a compressed signal containing only every Nth frame of the uncompressed play video and the fast reverse stream is a compressed signal containing every Nth frame of the uncompressed play video played backwards. To store the video information, each stream is divided into portions (e.g., N-byte segments of compressed data) and striped onto a disk array. The disk array stores all the information that the file server can directly access.
The process for generating the fast forward and fast reverse streams is performed in a non-real time manner such that the video content is pre-encoded and stored in the file server. The process requires a frame by frame analysis of the video stream to enable the frames to be encoded in an MPEG-2 compliant form, yet provide a fast forward and fast reverse effect when decoded. As such, the video sequence is processed to extract every Rth frame (i.e., one of every R frames, where R is an integer greater than 1) to form a fast forward sequence and then the fast forward sequence is encoded (compressed). For a fast reverse stream, a sequence of frames in reverse order is created and encoded. This encoding process can not be used for producing fast forward and fast reverse streams in real time such that a real time program can be encoded and stored for almost immediate use of VCR-like functions.
Therefore, there is a need in the art for an improved encoding system for a video-on-demand system to ensure near real-time availability of fast forward and fast reverse functions and real-time availability of a high bit rate video bitstream that, when decoded, produces a play sequence.